In processes in chemistry, biology and medicine, separating liquid streams often play an important role. There, it is often the case that in analyses and high-precision separation and dosing processes, highly thinned solutions are finely dosed using nozzles, pipettes or other equipment. Separating liquid streams also play an important role in the sorting of particles, for example, cells from living creatures, using cell sorters, as is described in Herzenberg, L. A., Sweet, R. G., Herzenberg, L. A., "Fluorescence-activated cell sorting," Sci Amer 234(3):108, March 1976. For these reasons, there is a strong desire to be able to automatically monitor such liquid streams with respect to their external parameters, that is, drop speed, drop size, drop distance, position of the separation point and their regularity. Currently, no devices and methods are known that ensure such an automatic monitoring.